Technical Field
The present disclosure relates to a method for manufacturing a crimp terminal serving to connect a wire harness for an automobile, the crimp terminal, and a wire harness.
Background
Wire harnesses are often used for internal wiring of automobiles. A wire harness is a module in which a plurality of coated wires are assembled in accordance with in-vehicle wiring specifications. Crimp terminals, for example, are crimped to ends of each of the coated wires. When connecting a crimp terminal to a wire end of the wire harness, electrical connection between the wire end and the crimp terminal is provided by stripping the insulating coating layer at a wire end to expose the core wire, and swaging and crimping a core wire barrel of the crimp terminal to the exposed portion of the core wire. The connecting portion between the crimp terminal and the wire end is sealed with resin so as to prevent corrosion of the core wire due to ingress of moisture into the wire from the connecting portion (see Japanese Laid-Open Patent Publication No. 2001-167821 and Japanese Laid-Open Patent Publication No. 2012-069449).
However, sealing the connecting portion of the crimp terminal and the wire end with resin gives rise to an increase in the manufacturing cost of the wire harness. This is because, in addition to the fact that the resin used is expensive in itself, time is required to apply and cure the resin in a resin molding process or a coating process.
Therefore, it is attempted to bend the electric wire connecting portion (the crimp portion) of the crimp terminal into a tubular shape by press molding, and then the entire butted interface on the plate ends that are formed in the portion bent into a tubular shape are laser-welded together. Subsequently, one end side of the portion bent into a tubular shape is laser-welded and sealed into a sealing portion to form a barrel member, to configure the electric wire connecting portion into a hermetically-closed structure.
However, the joining strength on the weld portion by laser welding depends mainly on an intensity and a sweep rate of the laser light radiated onto the weld portion. If the laser welding is performed outside the proper range of the parameters of the intensity and the sweep rate of the laser light, the joining strength on the weld portion of the crimp portion becomes weak. This causes cracks in the weld portion when crimping the crimp terminal to the electric wire terminals.
Especially, in a structure in which the core wire and the coating layer of the electric wire are sealed with a tubular barrel, the shape of the crimped core wire portion is significantly different from the shape of the crimped coating layer portion. This is because the core wire portions need to be formed into the most suitable shape to make the electrical conduction stable, whereas the coating layer portions need to be formed into an appropriate shape to prevent moisture from entering the inside of the tubular barrel from the gap between the crimp terminal and the electric wires. This brings a risk of cracking in the weld portion due to a complex force acting on the terminal when crimping the electric wires and the terminal together.
In addition, considering the mass productivity, high accuracy in determining the positions of the terminals and hence accuracy of welding is required since, for example, 400 terminals are welded per minute. In this regard, the possibility of high-quality laser welding by providing a certain level of width between the welding marks (weld bead) to weld the butted interface between the plate edges is becoming clearer. In other words, having a narrow weld bead requires a high degree of accuracy in determining the positions, which leads to a narrowing of the “process window” for treating the welded terminal. A wide weld bead, on the other hand, causes excessive melting of the weld portion as well as welding defects in multiple places.
The present disclosure is related to providing a method for manufacturing a crimp terminal which enables performing high-quality laser welding on a workpiece by controlling the intensity and the sweep rate of laser light to be radiated onto a weld portion to appropriate values. The present disclosure also provides the crimp terminal itself, and a wire harness having the crimp terminal.